Tire tread element mold chamfer to modify RCF and/or RSAT using the existing mold

ABSTRACT

A method and apparatus for modifying residual cornering force (RCF) or residual self-aligning torque (RSAT) of a tire 12. The tire mold 30 is modified by removing or adding removable chamfer mold pieces or material 50,150 to the interior surface of the tire mold 30. The removable chamfer mold pieces chamfer portions of the tire tread 10 at key locations, addition or deletion of such chamfer portions 50,150 at selected locations can modify the tire&#39;s RCF and/or RSAT parameters.

This is a division, of application Ser. No. 08/588,036, filed Jan. 17,1996.

BACKGROUND OF THE INVENTION

This invention pertains generally to the art of methods and apparatusesfor molding pneumatic tires, and more particularly to a tire moldfeature which creates chamfers on the edges of tire tread elements tovary the level of residual cornering force (also known as RCF) orresidual self-aligning torque (also known as RSAT) in tires produced bythe tire mold.

The chamfer feature may be built into a mold and then ground outwherever the chamfer is not desirable. Alternatively, the same effectcan be obtained by adding chamfer inserts to the interior of a mold.

At a tire's point of contact with a road, also known as the contactpatch, a tire experiences a moment about its vertical axis. This momentis referred to as a self-aligning torque. At a small slip angle wherethe self-aligning torque is zero, an additional horizontal force,referred to as residual cornering force, or RCF, is present. Even whenlateral forces such as those relating to plysteer and conicity arereduced to zero, residual self-aligning torque, or RSAT may remain.

The level of RCF and/or RSAT of a tire varies with the shape and profileof the individual elements of the tire tread. In the past, one methodemployed by tire designers to vary RCF and/or RSAT of a certain tiredesign was to obtain a new tire mold with alterations, which may haveincluded changes to the tire tread elements, to modify the originaltread pattern. Manufacturing a new mold can be costly and timeconsuming, thereby slowing the development of new tire designs.

Applicants recognized a need for a more cost-effective solution to theRCF and/or RSAT problem than redesigning and modifying entire existingmolds that produce tires with unacceptable RCF and/or RSAT. Applicantshave developed a new mold and tire made there from that enables the tiredesigner to change the RCF and/or RSAT in tires from a mold by addingchamfer inserts to the mold to create the chamfer in the tire or morepreferably by designing the mold with selected tread elements chamfered,and then modifying that mold to adjust the RCF or RSAT of the tire byselectively removing the mold material which created the chamfer.

The present invention contemplates a new and improved method andapparatus for modifying RCF and/or RSAT of a tire which is simple indesign, effective in use, and overcomes the foregoing difficulties andothers while providing better and more advantageous overall results.

SUMMARY OF THE INVENTION

In accordance with the present invention, a new and improved method andapparatus for modifying RCF and/or RSAT is provided which can beutilized with existing tire molds 30 or built into new molds.

The preferred invention includes a tire mold 30 for modifying theresidual cornering force or residual self-aligning torque of a tire 12.The mold 30 has a molding means for molding treads. The molding meanshas a plurality of recesses 38 for forming tread elements 22, each treadelement 22 having two or more edges 44. A plurality of the tread elementforming recesses 38 have one or more portions 150 for forming chamferededges 46 along the edge of the tread element 22 edges. Some of thechamfer forming portions 150 are selectively removed for modifying theresidual cornering force or self-aligning torque of the molded tire 12.In one mold 30 a majority of tread element forming recess are initiallyfabricated having a chamfer forming portion 150 at one or more edges 44of the respective tread element forming recess. The preferred method isto then choose predetermined chamfer forming portions 150 to modify theresidual cornering force or residual self-aligning torque and to removethe chosen predetermined portions 150 of the mold such that selectededges 44 of the tread elements 22 are partially or completelyunchamfered. Preferably the portions 150 are removed using a grindingprocedure. The chamfer portion 46 can extend circumferentially orlaterally or at any angle anywhere in between, depending on the angle ofthe tread element. The chamfer portion 46 as shown in FIG. 3 extendsgenerally laterally along the edge of tread element 22. For the purposeof this invention a chamfer portion extends along an edge 44 of thetread element 22, the edge 44 being the intersection of a groove walland the ground contacting surface 48 of the element 22. This chamferportion can enable the tire designer to alter or modify a tire'sperformance without requiring a new mold to be built.

More particularly, in accordance with the present invention, a method ofmolding a tire for modifying residual cornering force of a tire includesthe steps of providing chamfering means in the mold interior surface,measuring residual cornering force for tires produced by the tire mold,comparing measured residual cornering force for tires produced by thetire mold to a specification range, and selectively removing some or allof the chamfering means from the mold if measured residual corneringforce is outside the specification range, thereby, removing thechamfering of the tread elements of the tire, which alters the RCF levelof the tire.

According to another aspect of the present invention, the chamferingmeans comprises an insert insertable in the mold for chamfering an edgeof a tread of a tire.

According to another aspect of the present invention, a method formodifying residual self-aligning torque of a tire, the tire being moldedby a tire mold, the tire mold comprising a plurality of recesses forforming a tire tread, the method comprising the steps of measuringresidual self-aligning torque for tires produced by the tire mold,comparing measured residual self-aligning torque for tires produced bythe tire mold to a specification range, providing chamfering means forchamfering the tire tread produced by the tire mold if measured residualself-aligning torque is outside the specification range, and, chamferingthe treads.

According to another aspect of the present invention, an insert for usewith a tire mold for modifying residual cornering force or residualself-aligning torque of a tire, the insert comprising a first side and asecond side, a chamfer edge, the chamfer edge being disposed on thefirst side, and, attaching means for attaching the second side to thetire mold.

One advantage of the present invention is the ability to modify ratherthan replace a tire mold to adjust RCF and/or RSAT of a tire.

Another advantage of the present invention is to reduce tire developmentcosts by giving the tire engineer the capability of placing chamferinserts into the tire molds, rather than replacing the entire tire mold.

Another advantage of the present invention is time savings derived fromgiving the tire designer the capability of modifying existing molds,rather than having to design, build, and receive new tire molds.

Still other benefits and advantages of the invention will becomeapparent to those skilled in the art upon a reading and understanding ofthe following detailed specification.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may take physical form in certain parts and arrangement ofparts. A preferred embodiment of these parts will be described in detailin the specification and illustrated in the accompanying drawings, whichform a part of this disclosure and wherein:

FIG. 1 is a plan view of a portion of a tire tread extending between afirst tread edge and a second tread edge;

FIG. 2 is a cross-sectional view of a tire mold according to theinvention;

FIG. 3 is a plan view of the portion of the tire tread illustrated inFIG. 1 after application of the invention and FIG. 3A is a cross sectionof the tread taken along line 3A--3A of FIG. 3;

FIG. 4 is an enlarged view of a portion of the mold illustrated in FIG.2;

FIG. 5 is a perspective view of an insert according to the invention;

FIG. 6 is an enlarged view of a portion of a tire mold utilizing apreferred embodiment of the invention; and,

FIG. 7 is a graph showing some experimental results of tiresincorporating the invention.

FIG. 8 is a cross-sectional view of a control tire with no chamfering.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the drawings, which are for purposes of illustrating apreferred embodiment of the invention only, and not for purposes oflimiting the invention, FIG. 1 shows a portion of a tire tread 10 thatstretches across a tire from the first tread edge 14 to the second treadedge 18. Grooves 28 in the tread 10 channel water away from the contactpatch to improve traction on wet road surfaces. Between the grooves 28are tread elements 22 which extend radially outwardly of the tread 10.The tread 10 has sipes 26, or smaller grooves, to improve traction andother tire performance parameters.

With reference to FIGS. 1 and 2, the tire 12 and tire tread 10, isformed and vulcanized in the conventional manner by molding the tire 12in a tire mold 30. The tire 12 is vulcanized within the mold 30 duringthe curing process.

One important and commonly monitored aspect of tire performance is themagnitude of certain forces and torques generated by rotation of thetire 12 against the road surface. Two of these are referred to as"residual cornering force" (RCF) and "residual self-aligning torque"(RSAT). Because these forces and torques are well known in the tire art,only a brief discussion will be made here.

Although the lateral forces generated by a tire can be reduced to zerowith respect to a forward velocity vector at a small slip angle (calledthe neutral slip angle), RSAT remains about the axis vertical to thecontact patch of the tire. At a slip angle where self-aligning torque iszero, a lateral force, RCF, exists and may cause the tire to drift in alateral direction. RCF or RSAT may be affected by the shape and designof the tread 10. RCF or RSAT may be reduced or increased by chamferingor otherwise modifying certain areas of the tire treads elements 22.

FIG. 2 shows a cross-sectional view of a schematic of a tire mold 30.The right side of the tire mold 30 in FIG. 2 is shown with a tire 12mounted therein while, for ease of illustration, the left side of thetire mold 30 is shown without the tire 12. The interior surface of thetire mold 30 is the negative impression of the tire tread 10. Becausethe tire mold 30 is the negative impression of the molded tire tread 10,recesses 38 in the tire mold 30 form the radially-protruding treadelements 40 in the tread 10. Likewise, the protruding extensions 42 inthe tire mold 30 form the grooves 28 in the tire around the tread 10.

RCF or RSAT may be adjusted and controlled by chamfering or bevelingcertain portions of the tire tread 10. FIG. 3 shows a tire tread 10 withcertain edges 46 chamfered. The chamfering of the edges 46 can affectthe RCF and/or RSAT levels in the tire. In the specific treadconfiguration of FIG. 3, chamfering the edges 46 creates a negativeshift in the tire RCF and/or RSAT level. Tire treads 22 may be chamferedby grinding the tire after unacceptable levels of RCF and/or RSAT havebeen measured, but such grinding is costly and time-consuming.

Tire RCF and/or RSAT can be modified by using a mold with a modifiedtread pattern, but the design and manufacture of a new tire mold takes asignificant period of time. This delay could idle expensive productionequipment and delay the delivery of the finished product to theconsumer. The invention herein described eliminates both of theseexpensive and time-consuming alternatives by providing a third andfourth alternative. In the third alternative, inserts 50 are placedwithin an existing tire mold to modify the RCF and/or RSATcharacteristics of a tire. As illustrated in FIGS. 2, 4 and 5, theinserts 50 may be mounted into a tire mold 30 using any acceptablemounting means, including adhesives or mechanical fasteners such as abolt or screw 56.

With reference to FIG. 5, a typical insert 50 is shown. The insert 50has a first side 64, a second side 66 and a chamfer side 60. The chamferside 60 is the portion of the insert 50 which contacts the tire tread 10in the mold 30 during the curing process and alters the shape of thetire tread 10. In the preferred embodiment, the insert 50 includes ahole or bore 70 through which an associated screw 56 or bolt can bereceived for securing the insert 50 to the tire mold 30.

Another important advantage of the invention is the savings in tiredevelopment time. Also, the cost of tire development may be reduced by adecrease in hardware costs, such as the cost of a new tire mold 30.Finally, the tire inserts 50 may be used in tire production molds 30 toslightly alter existing tire type production to bring production tireswithin industry specifications for RCF and/or RSAT.

With reference to FIG. 4, the inserts 50 are typically made of the samematerial as the mold with which they are intended to be used. Forexample, one preferred material for the inserts 50 is aluminum. Theangle α that the chamfer surface 60 of the insert 50 makes with the tiremold's surface 38 is chosen for each tire application, but is generallybetween 40 degrees and 85 degrees. While the insert 50 has been shown asmounted in the outermost recesses 38 of the tire mold 30, inserts 50 canbe utilized in any portion of the tire mold 30, and inserts 50 can beused in multiple recesses 38 of a tire mold 30 at the same time.

With reference to FIG. 6, in the fourth and preferred alternative, thetire mold 30 is originally produced with chamfering means for chamferingthe tread elements. The chamfering means takes the form of mold portions150 which are located in the tire mold at points where a chamfer mightbe later required. Preferably, a number of the edges of the tire treadelements 22 are chamfered as the edges 46 in FIG. 3. To adjust or modifyRCF and/or RSAT, selected mold portions 150 may be partially or entirelyremoved from the mold by grinding the mold portions 150 out of the tiremold 30 along dotted line 152. This has essentially the same effect ofaltering the tire RCF and/or RSAT as adding inserts 50 as describedabove, but is generally more efficient for the tire manufacturing anddevelopment process.

In either inventive approach it will be appreciated that the resultantchamfer portion 46 need not and preferably does not extend to the fulldepth of the tread element 22. The tread elements 22 when new have amore flexible structure which is believed to be a factor which caneffect the RCF or RSAT more dramatically when the tread is new and atfull depth. As the tire wears the effect of RCF or RSAT as it relates totread element flexibility is reduced. Therefore, the chamfer portion 46must perform its modifying RCF or RSAT function most when the tread isnew. As the tread elements 22 wear down, the chamfer portion 46decreases in size to the point of nonexistence. As this occurs, theground contacting surface 48 of the element 22 increases tending toretard the rate of tread wear. This feature is considered an importantbenefit on those treads 10 where the RCF and RSAT modificationrequirements diminish as a function of increased tread wear.

With reference to FIG. 7, tires incorporating the invention havedemonstrated excellent results. In FIG. 7, the term "CONT" refers to acontrol tire, the term "OSSH" refers to the tire's outside shoulder, theterm "TRAIL" refers to the trailing edge of an element, the term "LEAD"refers to the leading edge of the element, and the term "RCF" refers toresidual cornering force. The "y axis" of the graph lists the force ofthe RCF in newtons. Experimental test results utilizing a Goodyear Tireand Rubber Company Eagle RS-A tires of size P205/55R16 tires areillustrated. In each case discussed herein or illustrated in FIG. 7, theterminology is defined as looking at a tire mounted on the right handside of a vehicle.

As illustrated in FIG. 7, tread elements having no chamfering was acontrol tire and generated RCF values in the amount of about 30 newtons.The chamfers were 2 mm by 2 mm at an α angle of 45°.

Tread elements having similar chamfering on the tire's outside shoulder,trailing edge produced a moderate negative shift in the RCF value in theamount of 15 to 35 newtons.

Tread elements having chamfering on the tire's inside shoulder, trailingedge produced a moderate positive shift in the RCF value in the amountof about 43 newtons.

Using a combination of the above chamfer locations provides thecapability to increase or decrease the RCF or RSAT characteristics ofthe tire.

Tread elements having chamfering on the tire's inside shoulder, leadingedge produced a moderate negative shift in the RCF value in the amountof about 30 newtons.

The above described test results, along with FIG. 7, demonstrates thatthe invention is effective to modify, either in the positive or negativedirection, a tire's RCF values.

The invention has been described with reference to the preferredembodiment. Obviously, modifications and alterations will occur toothers upon a reading and understanding of the specification. It isintended by applicant to include all such modifications and alterationsinsofar as they come within the scope of the appended claims or theequivalents thereof.

Having thus described the invention, it is now claimed:

What is claimed is:
 1. A method for modifying residual cornering forceor residual self-aligning torque of a tire, said tire to be molded by atire mold, said tire mold for forming treads on the surface of saidtire, said tire mold forming tread elements on the surface of a tread ofsaid tire, said tread elements having tread edges, said mold having aplurality of selectively removable insert portions effective to chamfersaid tread edges, said method comprising the steps of:choosingpredetermined insert portions to modify the residual cornering force orresidual self-aligning torque of said tire, and; removing thepredetermined insert portions of said mold such that selected edges ofsaid tread elements are unchamfered partially or completely.
 2. Themethod for modifying residual cornering force or residual self-aligningtorque of tires of claim 1 further comprising the steps of:measuringresidual cornering force of a first tire produced by said tire mold;comparing the measured residual cornering force for sa id first tireproduced by said tire mold to a specification range of residualcornering force; removing an insert portion of said tire mold if themeasured residual cornering force is outside the specification range;molding a second tire in said mold; measuring residual cornering forceof said second tire produced by said tire mold; comparing the measuredresidual cornering force for said second tire produced by said tire moldto a specification range of residual cornering force; and, removingadditional insert portions of said mold until the measured residualcornering force is within the specification range.
 3. A method formodifying residual cornering force or residual self-aligning torque oftires, said tires to be molded by a tire mold, said tire mold comprisinga plurality of recesses for forming treads on the surface of said tires,said method comprising the steps of:measuring residual cornering forceof a first tire produced by said tire mold; comparing the measuredresidual cornering force for said first tire produced by said tire moldto a specification range of residual cornering force; installing achamfering means for chamfering said treads in said tire mold if themeasured residual cornering force is outside the specification range;molding a second tire in said mold; measuring residual cornering forceof said second tire produced by said tire mold; comparing the measuredresidual cornering force for said second tire produced by said tire moldto a specification range of residual cornering force; and, adjustingsaid chamfering means until the measured residual cornering force iswithin the specification range.